The invention relates to a plant for medical air production on-site, that is to say in a hospital building or the like, employing a three-way solenoid valve adapted to discharge product gas contaminated by impurities to the atmosphere via a purge line connected to one of the ports of the solenoid valve, and to a method for controlling or operating such a plant.
The medical air used in hospitals, clinics, treatment centres, emergency or incident units, or the like, for patients' respiration is a medicament whose composition is specified by the European Pharmacopoeia.
More precisely, medical air is ambient air compressed to a pressure above atmospheric pressure, typically several bars, or to tens or even hundreds of bars and containing (by volume) from 20.4% to 21.4% oxygen, at most 500 ppm CO2, at most 5 ppm CO, at most 1 ppm SO2, at most 2 ppm NO and NO2, at most 67 ppm water and at most 0.1 mg/m3 oil; the oil vapours possibly present essentially come from the compression of the air.
It should be noted that, other than oxygen, the components mentioned above (i.e. COx, NOx, water, or oil etc.) are in fact impurities whose presence is tolerated within the limits of the Pharmacopoeia but which ideally are not present therein.
Medical air furthermore contains nitrogen, and may also contain other compounds, such as argon.
Currently, medical air is delivered to hospitals or the like in three forms, namely, depending on the case:                direct delivery in the form of compressed air, for example at an absolute pressure of from 200 to 300 bar, in cylinders, that is to say bottles or canisters of gas, or containers comprising a plurality of bottles;        production on-site by mixing oxygen and nitrogen so as to create nitrogen/oxygen mixtures, and        direct production on-site from ambient air treated, in particular, by compressors and filtration/purification systems.        
Of these, the production of air directly on-site by compressors and filtration systems is the most widespread solution. Such a method is described, for example, in the document EP-A-864818.
The ambient air is taken in and compressed by compressors to a pressure range extending from 1 bar to 80 bar relative. This compressed air is then filtered, that is to say purified, by means of one or more treatment steps, for example by a set of filters and/or by employing a pressure swing adsorption method (PSA).
The medical air produced in this way may be stored in one or more intermediate buffer vessels, then sent through the network of pipes which passes through the hospital building in order to provision the treatment rooms, bedrooms or the like with medical air. It is quite clearly possible, and even indispensable in certain cases, to carry out intermediate expansion of the gas, for example in order to change from a pressure of about 10 bar in the storage vessel to a pressure of 5 or 8 bar in the network.
In general, any break in medical air provision is overcome by using medical air taken from a reserve or backup source in which the air is kept in gaseous form.
The other medical gases used in hospitals or treatment centres, such as oxygen, are also delivered in a similar way to the air. The compositions of these other gases are also specified by the European Pharmacopoeia.
Thus, oxygen may also be produced on-site by a PSA method by using specific adsorbents, such as lithium-exchanged zeolites X, making it possible to retain the nitrogen contained in the air and thus produce gaseous oxygen having a purity typically greater than 90%, or even 93% by volume, as is known from the document EP-A-297542.
However, the methods for producing medical air or other medical gases used on-site (also referred to as on-site methods) present certain drawbacks.
First, these methods do not permit easy monitoring of the reliability of the manufacturing process.
Thus, when an on-site medical air production unit is operating autonomously, the manufacturing process is not overseen continuously and the interventions on the plant take place on the basis of planning, that is to say preventive maintenance, or when an error or a problem arises in the plant, that is to say curative maintenance.
These interventions are therefore carried out independently of the status of the plant and its reliability, which is not optimal because they are carried out either too soon, and therefore without actual need, or too late, and therefore with an impact on the production process and possibly on the final product.
Next, pollutant blockages in the main pipe occur when the gas produced is not compliant. This is because in existing plants, the control solenoid valve is a so called “2-way” solenoid valve which is arranged on the main line.
Although it makes it possible to stop possible pollution upstream of the valve, this pollution nevertheless remains blocked in the main line and necessitates a total purge of the system upstream of the valve. This is not ideal because it entails a shutdown of the gas production and manual intervention.
Furthermore, in the event of short-term breaks in the air provision due, for example, to temporary contamination at the inlet, the backup source is resorted to directly. However, this poses a problem because the backup volume is limited and therefore, if the frequency of the breaks in provision is high, there is then a risk of draining the backup source. In other words, it would be highly beneficial to be able to avoid this drawback by reducing the extent to which the backup source is used, so as to increase its autonomy over time.
Lastly, the air produced by the current methods and plants is in general neither analyzed nor validated in pharmaceutical terms, which may raise obvious problems of compliance and quality. Furthermore, when it is analyzed, in the event of “noncompliance” this usually leads either to immediate interruption of the production and changeover to a backup source air, which may entail overuse of the backup air liable to cause a possible total break in the air provision, or to continuous provision of noncompliant air and parallel triggering of an alarm in order to warn the user, who then needs to intervene manually. It will be understood that these solutions are not ideal either.
In summary, there is currently no method of validating air produced on-site which makes it possible to ensure that the air produced is in fact compliant with the required specifications and which makes it possible to ensure effective and reliable provision of medical air.
In other words, the problem which arises is to provide a plant for continuous on-site production of a medicament gas, particular medical air, in accordance with good manufacturing practice (GMP) and a method for controlling or operating such a plant, which permit in particular:                supervision of the reliability of the manufacturing process with rapid detection of any anomaly,        monitoring of the various production steps and in particular the final production with, for each step, the possibility of a purge thus making it possible to stop any contamination or noncompliance of the gas produced, in particular medical air, and/or        the use of the backup sources to be reduced to a minimal level.        